1. Field of the Invention
The present invention relates to improvement of an automatic document feeding apparatus mounted on a recording apparatus of an electrophotographic reproducing machine and others.
2. Description of the Prior Art
The automatic document feeding apparatus is generally mounted for use on a document glass plate (platen glass). In a reproducing machine using a movable optical system on which this automatic document feeding apparatus is mounted, documents in sheets (hereinafter referred to simply as documents) of standard sizes (for example, JIS Standard A series, B series, or USA Standard sizes) are stacked on a document stacker (stacking section), and each sheet of the documents is fed out one by one from the stack by feed rollers and others of the automatic document feeding apparatus and is carried by a carrier belt onto the document glass plate where exposures of a given number of copies are conducted with an exposure lamp equipped in the body of the reproducing machine. Then, each of the documents is delivered onto a document delivery tray.
Conventionally, in the operation of replacing documents on the document glass plate the next document is fed out from the stack after a delivery sensor has detected the delivery of the preceding document from the document glass plate. Then, this next document is carried to the document glass plate and placed at a given position thereon. Thus, it takes a long time to complete replacing the document. Hence, the copy processing time becomes elongated.
Copy productivity will drop because of the document replacement operation on the document glass plate in such an automatic document feeding apparatus unless the feeding and ejecting of the documents are executed in a short period. In other words, it is desirable that the copy processing speed CPM (number of copies processed per minute) of the image forming process on the reproducing machine main side is substantially equal to the document processing speed OPM (number of documents conveyed per minute) of the automatic document feeding apparatus.
However, in a case where documents are automatically fed and delivered onto the document glass plate for replacement using an automatic document feeding apparatus, the productivity of copying documents becomes 100% and no wasteful time is consumed, if the replacement of the documents is performed during the period in which the scanning optical system is returned to its home position.
In a reproducing machine capable of high speed copy processing, the document replacement time is reduced by increasing the document conveying speed from a document double-feed prevention position in the stack portion to the document stop position on the document glass plate surface and the ejecting speed of ejecting the document from the document stop position to the outside of the machine. Further, another method of reducing the document replacement time has been employed which starts the feed of the next document on the document placement table almost at the same time of the start of the ejection operation of the document which has been subjected to image exposure.
Therefore, the document conveying speed from the document double-feed prevention position of the stack portion to the document stop position on the document glass plate surface must be raised.
When the document conveying speed is increased, however, there occur various problems such as the use of a greater motor, the increase in power consumption, the increase in damages of the documents, the drop of document separability, and so forth.
In order to further shorten the document replacement time and to improve the document processing speed (OPM), an automatic document feeding apparatus for conveying a sheet-like document to an image exposure portion, stopping the document at the image exposure portion, moving an optical system to make scanning exposure and delivering the document after exposure to a document ejection table is proposed. Such automatic document feeding apparatus comprises a first driving system consisting of feed rollers for feeding the document to an intermediate conveyor roller and to the image exposure portion and of separation means and a second driving system for conveying, stopping and ejecting the document onto, at and from the image exposure portion by a conveyor belt or the like, in which the first driving system is driven within at least part of the exposure time during which the document is stopped at the predetermined position of the image exposure portion and is subjected to scanning exposure, so that at least part of the feeding operation of the next document is made.
In such an automatic document feeding apparatus, the second driving system has a certain time lag from the start of driving till it operates at a predetermined speed. Accordingly, if the trailing edge of the document completely leaves the intermediate conveyor roller for feeding the document into the image exposure portion before the document reaches the image exposure portion, is sufficiently pressed by the conveyor member and conveyed reliably at a predetermined speed; the conveyance of the document becomes unstable, and there occur conveyance failures such as jamming of the document, and failure of arrival of the document at the predetermined stopper position. These problems are serious particularly in the case of documents having small sizes (e.g. B5; transverse position, 182 mm long).